Limited influence of tillage management on organic matter fractions in the surface layer of silt soils under cereal-root crop rotations

It has been shown that reduced tillage (RT) management may increase the surface soil organic carbon (SOC) and nitrogen (SN), particularly due to accumulation of labile organic matter (OM). However, only few studies have focused on cereal-root crop rotations under a temperate climate which cover a large part of Northwestern European cropland. We investigated the effect of RT compared with conventional tillage (CT) on the distribution of SOC and SN over different soil fractions from seven pairs of fields with cereal-root crop rotations, located in the Belgian loess belt. Surface soil samples (0-100 mm) were physically fractionated according to a sequential sieving and density separation method into stable microaggregate, silt and clay and free and occluded POM fractions. RT management was previously found to be effective in increasing the organic carbon (OC) and organic nitrogen (N) content of the surface soil (0-100 mm) at these seven sites. Here, physical fractionation showed that the difference in amount of OC and N in free particulate OM (fPOM), intra-microaggregate particulate OM (iPOM) and silt and clay associated OM between the RT and CT soils contributed 34, 29 and 37% of the increase in SOC and 35, 32 and 33 % of the increase in N. The contribution of OC and N in iPOM and fPOM increased significantly on a relative basis under RT management. Only a modest increase of iPOM and slight enhancement of microaggregation was observed in the RT compared to the CT soils. We suggest that the repeated disturbance of soil by harvest of root crops and repeated use of cultivators and harrows may limit the accumulation of physically protected POM under RT management of these Western-European cereal-root crop rotations. Instead most of the accumulated OC and N in the surface horizons under RT management is present as free unprotected POM which could be prone to rapid loss after (temporary) abandonment of RT management.

@article{956439,
abstract = {It has been shown that reduced tillage (RT) management may increase the surface soil organic carbon (SOC) and nitrogen (SN), particularly due to accumulation of labile organic matter (OM). However, only few studies have focused on cereal-root crop rotations under a temperate climate which cover a large part of Northwestern European cropland. We investigated the effect of RT compared with conventional tillage (CT) on the distribution of SOC and SN over different soil fractions from seven pairs of fields with cereal-root crop rotations, located in the Belgian loess belt. Surface soil samples (0-100 mm) were physically fractionated according to a sequential sieving and density separation method into stable microaggregate, silt and clay and free and occluded POM fractions. RT management was previously found to be effective in increasing the organic carbon (OC) and organic nitrogen (N) content of the surface soil (0-100 mm) at these seven sites. Here, physical fractionation showed that the difference in amount of OC and N in free particulate OM (fPOM), intra-microaggregate particulate OM (iPOM) and silt and clay associated OM between the RT and CT soils contributed 34, 29 and 37\% of the increase in SOC and 35, 32 and 33 \% of the increase in N. The contribution of OC and N in iPOM and fPOM increased significantly on a relative basis under RT management. Only a modest increase of iPOM and slight enhancement of microaggregation was observed in the RT compared to the CT soils. We suggest that the repeated disturbance of soil by harvest of root crops and repeated use of cultivators and harrows may limit the accumulation of physically protected POM under RT management of these Western-European cereal-root crop rotations. Instead most of the accumulated OC and N in the surface horizons under RT management is present as free unprotected POM which could be prone to rapid loss after (temporary) abandonment of RT management.},
author = {Kader, MD Abdul and Sleutel, Steven and D'Haene, Karoline and De Neve, Stefaan},
issn = {0004-9573},
journal = {AUSTRALIAN JOURNAL OF SOIL RESEARCH},
keyword = {Arable Loess Soil,Long-term Field Experiment,Soil Organic Matter,Physical Fractionation,Conservation Tillage,LAND-USE,PARTICLE-SIZE FRACTIONS,NO-TILL,PHYSICAL FRACTIONATION,CONSERVATION TILLAGE,GRASSLAND SOILS,LOAM SOILS,NITROGEN,ACCUMULATION,CARBON SEQUESTRATION},
language = {eng},
number = {1},
pages = {16--26},
title = {Limited influence of tillage management on organic matter fractions in the surface layer of silt soils under cereal-root crop rotations},
url = {http://dx.doi.org/10.1071/SR09052},
volume = {48},
year = {2010},
}